【作者】 张腾；

【导师】 蔡宁生；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2010， 硕士

【摘要】 化石燃料燃烧产生的CO₂是最主要的温室气体来源,O₂/CO₂循环燃烧是一项非常有潜力的碳捕集技术,而且特别适合于我国以煤为主的能源结构。O₂/CO₂循环燃烧需要空分制氧,会使常规电站的净效率大幅下降。目前的几种空分制氧方式均是制纯氧,制氧系统投资大,能耗高。针对O₂/CO₂循环燃烧实际所需的仅是O₂浓度为20-40%的O₂-CO₂混合气这一特点,本文研究了采用化学链方式直接制取这种混合气以降低制氧能耗。采用浸渍担载法制备了钴基制氧剂颗粒,通过XRD分析了颗粒成分,通过SEM观察了颗粒微观结构。在TGA上研究了制氧剂颗粒在不同温度下和不同氧浓度下的吸氧特性以及在CO₂气氛下的解吸特性。实验结果显示制氧剂颗粒不会与CO₂发生反应,吸氧和解吸反应速率较好,通过不同氧浓度下的初始分解温度获取了钴基制氧剂的热力学平衡关系式,采用缩核模型对动力学特性进行了研究并获取了动力学参数。针对钴基制氧剂熔点低可能会发生烧结的质疑,在制氧所需要的高温下进行了150次吸氧解吸循环反应,循环稳定性非常好,没有任何衰减现象。对烟气中的SO₂,NO可能对制氧剂的影响进行了实验验证及理论分析,说明了实际烟气用于解吸过程吹扫气的可行性。在固定床上交替进行了吸氧和解吸实验,研究了反应温度、空气流量和CO₂吹扫气体流量等因素对吸氧特性和O₂释放特性的影响。在双固定床上采用气路切换的方式,连续12个小时获得O₂浓度在20%以上的O₂-CO₂混合气,验证了连续制氧的可行性。通过对制氧过程的热力学平衡和热量分析,提出了适合钴基制氧剂的制氧系统和合适的运行参数,利用Aspen软件计算了制氧过程中的功耗和热量,计算结果表明相对于传统的深冷法制氧有很大优势。对制氧过程所需的制氧剂用量进行了评估,从成本和矿物储量方面论证了可行性。更多还原

【Abstract】 CO₂ emission from the combustion of fossil fuel is the main source of greenhouse gases. Oxy-combustion is a very promising CO₂ capture technology, which is particularly suited to the coal-dominated energy structure of China. However, the net efficiency of power station based on oxy-combustion will significantly decline due to the air separation unit. How to apply oxygen is a key barrier to the implementation of oxy-combustion. Presently all air separation technologies produce pure oxygen, thus have the disadvantages of heavy investment cost and high energy consumption. Based on the fact that an O₂-CO₂ mixed stream with O₂ concentration between 20-40% rather than pure oxygen is needed for oxy-combustion, this paper studied a chemical looping method that directly produces this kind of O₂-CO₂ mixed stream to reduce energy consumption.Co-based oxygen carrier particles were prepared by dipping method, then XRD were used to study their compositions and SEM were used to observe their micro-structures. TGA experiments were conducted to study their oxygen absorption and desorption characteristics under different temperatures and different O₂ concentrations. The results indicated that this kind of particles did not react with CO₂, and it had quite good react rate for both absorption and desorption process. A relation between O₂ equilibrium pressure and temperature were obtained by thermodynamic calculations and experimental data, and shrinking-core model were used to study the kinetic parameters. Co-based oxygen carrier had been doubted that it’s had low melting point and thus easy to deactivate due to sintering. In reply to this doubt, 150 cycles of absorption and desorption were conducted under high temperatures required by the oxygen process, very high cyclical stability were observed without any deactivation. Experiments and theoretical analyses indicated that the SO₂ and NO in the flue gas would have no effect on Co-based oxygen carrier under process temperatures, thus validated the feasibility to use flue gas as the purge gas.Absorption and desorption experiments were also conducted in fixed-bed reactor, to study the effects of temperature and gas flow rate on the absorption and desorption characteristics. O₂-CO₂ mixed stream with O₂ concentration above 20% was produced continuously for 12 hours in two parallel fixed-bed reactors using gas switch, validated the feasibility of continuous O₂ production.O₂ production system and operation parameters suited to Co-based oxygen carrier were proposed based on thermodynamic equilibrium and heat analyses. Then work and heat consumed in the oxygen process were calculated by Aspen, the results showed significant advantage compared with cryogenic oxygen method. The quantity of Co-based oxygen carrier needed for oxygen process was estimated to check the feasibility on costs and mineral reserves.更多还原